This invention relates to downhole equipment for use in the gas and oil drilling industry.
It is a frequent requirement of the gas and oil drilling industry to cut and remove sections of a wellbore casing. Typically, a casing cutter having extendable cutting blades is run into the wellbore and located adjacent the section of casing to be severed. The cutter is rotated and the cutting blades extended so as to engage the inner casing surface. Extension of the cutting blades continues until the blades completely penetrate the casing to create two separate casing portions. The uphole casing portion may be then removed from the wellbore as necessary.
On occasions, there is also a requirement to cut a wellbore casing whilst maintaining the portion of casing located below the cut in a state of tension. However, adequate means for satisfying this requirement has not previously been available.
It is an object of the present invention to provide apparatus for allowing a casing to be severed whilst maintaining a portion of casing below the region of severing in a state of tension.
It is a further object of the invention to provide such apparatus which is also compatible with a conventional casing cutter.
The invention provides apparatus for use in a wellbore, the apparatus comprising a first elongate member provided with at least one tooth, a second elongate member provided with at least one tooth; the first and second elongate members being arranged in telescopic relation to one another so as to be moveable relative to one another in a longitudinal direction between a retracted position, in which the at least one tooth of the first elongate member is engaged with the at least one tooth of the second elongate member so as to prevent relative rotation between said elongate members, and au extended position, in which the at least one tooth of the first elongate member is completely disengaged from the at least one tooth of the second elongate member so as to permit relate rotation between said elongate members and abutment surfaces of said elongate members are in mechanical communication with each other so as to prevent further extending longitudinal movement of said elongate members and thereby permit the transmission of a tension force through the apparatus via mean provided on each of the first and second elongate members for connecting said members, when in use, to additional apparatus.
In use, a conventional casing cutter may be attached uphole of the aforementioned apparatus (a xe2x80x9ctension swivel subxe2x80x9d) to one of the elongate members (e.g the first elongate member) whilst a casing spear is attached downhole of the apparats to the other of the elongate members (e.g. the second elongate member). The resultant cutting sting may be then run into a wellbore and located at the required depth. The casing spear may be set by means of an appropriate string rotation which is transmitted to the spear through the engagement of the elongate member teeth. Once the spear has been set so as to grip the wellbore casing, an uphole force may be applied to the string which moves the elongate member from the retracted position to the extended position. The abutment surfaces of the elongate members are thereby placed in mechanical communication with each other, and as a result, the uphole force places the region of casing located below the spear in a state of tension. Furthermore, movement of the elongate members into the extended position disengages the teeth thereby allowing free rotation of the elongate member attached to the casing cutter and the cutting string located thereabove. Thus, the casing cutter may be then rotated so as to sever the wellbore casing. Once the cutting operation has been completed, the uphole force on the cutting string, and accordingly the tension in the casing below the spear, may be slowly reduced to zero. The teeth of the elongate members are then re-engaged so as to permit rotation of the elongate member attached to the spear and thereby release the spear from the wellbore casing.
Preferably, biasing means is provided to bias the first and second elongate members into the retracted position. The biasing means is ideally a spring which may be located between the abutment surfaces of said elongate members. It is preferable for the spring to have sufficient stiffness to maintain the elongate members in the retracted position when, during use, the apparatus is placed in a state of tension due to the suspension of downhole equipment from said apparatus. Furthermore, a bearing is preferably located between the abutment surfaces of said elongate members. The first and second elongate members are preferably each provided with a multiplicity of teeth.
Thus, the apparatus of the invention provides means for setting a spear and for holding a casing and cutting sting in tension while the casing is severed above the spear by means of a conventional rotary casing cutter. Furthermore, once the casing has been cut, the tension in the casing and cutting string may be reduced in a controlled mariner and the spear may be thereby conveniently released.